Sodium‐ion batteries (SIBs) have gained tremendous interest for grid scale energy storage system and power energy batteries. However, the current researches of anode for SIBs still face the critical issues of low areal capacity, limited cycle life, and low initial coulombic efficiency for practical application perspective. To solve this issue, a kind of hierarchical 3D carbon‐networks/Fe7S8/graphene (CFG) is designed and synthesized as freestanding anode, which is constructed with Fe7S8 microparticles well‐welded on 3D‐crosslinked carbon‐networks and embedded in highly conductive graphene film, via a facile and scalable synthetic method. The as‐prepared freestanding electrode CFG represents high areal capacity (2.12 mAh cm−2 at 0.25 mA cm−2) and excellent cycle stability of 5000 cycles (0.0095% capacity decay per cycle). The assembled all‐flexible sodium‐ion battery delivers remarkable performance (high areal capacity of 1.42 mAh cm−2 at 0.3 mA cm−2 and superior energy density of 144 Wh kg−1), which are very close to the requirement of practical application. This work not only enlightens the material design and electrode engineering, but also provides a new kind of freestanding high energy density anode with great potential application prospective for SIBs.
Li‐rich manganese based oxides (LRMOs) are considered an attractive high‐capacity cathode for advanced Li‐ion batteries; however, their poor cyclability and gradual voltage fading have hindered their practical applications. Herein, an efficient and facile strategy is proposed to stabilize the lattice structure of LRMOs by surface modification of polyacrylic acid (PAA). The PAA‐coated LRMO electrode exhibits only 104 mV of the voltage fading after 100 cycles and 88% capacity retention over 500 cycles. The structural stability is attributed to the carboxyl groups in PAA chains reacting with oxygen species on the surface of LRMO to form a uniform and tightly coated film, which significantly suppresses the dissolution of transition metal elements from the cathode materials into the electrolyte. Importantly, a H+/Li+ exchange reaction takes place between the LRMO and PAA, generating a proton‐doped surface layer. Density functional theory calculations and experimental evidence demonstrates that the H+ ions in the surface lattice efficiently inhibit the migration of transition metal ions, leading to a stabilized lattice structure. This surface modification approach may provide a new route to building a stable Li‐rich oxide cathode with high capacity retention and low voltage fading for practical Li‐ion battery applications.
Propylene carbonate (PC) ‐based electrolytes have many desirable advantageous properties compared to the currently used ethylene carbonate (EC) ‐based electrolytes for lithium ion batteries, however, their poor compatibility with the graphite anode hinders its applications. Here, a facile and effective strategy to make electrochemically compatible PC‐based electrolytes by use of a weakly coordinating diethyl carbonate co‐solvent to induce PF6− anions into the solvation shell of Li+ to form an anion‐induced ion–solvent‐coordinated (AI‐ISC) structure is reported. Such an AI‐ISC structure can lead to an increase of the lowest unoccupied molecular orbital energy level of the electrolyte, therefore considerably improving the reduction tolerance of the PC solvent. Furthermore, by using the film‐forming additive (fluoroethylene carbonate, FEC), an electrochemically stable, EC‐free PC‐based electrolyte, which enables reversible Li+ intercalation on the graphite electrode is obtained. The graphite/LiNi0.5Mn0.3Co0.2O2 pouch cells using this PC‐based electrolyte exhibit very similar room‐temperature electrochemical performance to those using conventional EC‐based electrolytes and excellent low‐temperature performance. This work provides a new approach to make EC‐free electrolytes with a similar AI‐ISC structure but without the need for a high concentration of Li salt of highly concentrated electrolytes, which may bring new insights in the development of advanced electrolyte systems for wide battery applications.
A synergistic effect induced ultrafine-SnO2/graphene nanocomposite is synthesized via a simple method as an advanced lithium/sodium-ion batteries anode material.
Emerging rechargeable sodium-metal batteries (SMBs) are gaining extensive attention because of the high energy density, low cost, and promising potentials for large-scale applications. The mechanism investigation and performance optimization of SMBs are of great significance for fundamental science and practical applications. Consequently, this review provides fundamental insights into the cell chemistry and recent progress on several representative SMBs, including Na-O 2 , Na-CO 2 , Na-SO 2 , and room-temperature Na-S batteries, for which the Na-storage mechanisms, potential solutions for enhancing battery performance, and future perspectives are discussed. We emphasize the importance and challenges of sodium-metal anodes, as well as summarize and highlight feasible strategies to address the challenging issues facing them. Combined with current research achievements, this review offers future research directions from the viewpoint of better SMB full cells regarding cathode design and anode protection with compatible electrolyte systems.
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